1. Field of the Invention
The present invention relates to an optical information recording medium for recording/reproducing information by irradiating laser beams, and a method of manufacturing the same and particularly, to an optical information recording medium which has an optical information recording layer on a substrate and a light-transmissible layer on the optical information recording layer and carries out recording and reproduction of information by irradiating laser beams from a light-transmissible layer side, and a method of manufacturing the same.
2. Description of the Related Art
A method of increasing the numerical aperture (NA) of an objective lens for focusing laser beams to perform recording/reproduction of information is known as means of enhancing the surface recording density of an optical disk (disc). The increase of the numerical aperture (NA) reduces the width of the laser beam to be focused onto the disk, and thus information having high density can be recorded/reproduced. NA used to reproduce a conventional compact disk (CD) is equal to 0.45, however, an optical head having NA=0.6 is used for reproduction of a digital versatile disk (DVD). Further, there has been recently proposed an optical head whose NA is increased to 0.8 or more. If NA is increased, there would occur such a disadvantage that the permissible amount of aberration occurring due to an angle (tilt angle) at which the surface of the substrate is misaligned from the vertical direction with respect to the optical axis of the focused laser beam is reduced Therefore, it is preferable that the thickness of the substrate is as small as possible when NA is equal to a high value. For example, the thickness of the substrate is set at 1.2 mm (millimeter) for CD, however, it is set at 0.6 mm for DVD. In such a case that NA is increased to 0.8 or more, there is used a method of forming an optical information recording layer on a substrate and then forming a light-transmissible layer of about 0.1 mm in thickness to record/reproduce information from the light-transmissible layer side.
As a method of forming a light-transmissible layer is known a method of adhesively attaching a transparent film onto a recording layer through an adhesive layer such as a pressure-sensitive adhesive sheet, as disclosed in Japanese Laid-open Patent Publication No. Hei-11-273147. However, when this method is applied to an optical information recording medium having a recording layer formed of a phase change recording layer or an optical information recording medium having a recording layer formed of a dye-based recording layer on which only one recording is possible, there occurs such a disadvantage that thermal deformation occurs due to irradiation of laser beams when initialization or information recording is carried out, so that noises are greatly increased.